The present invention relates to the transfer of a liquid coolant from a stationary member to a rotating apparatus and, more particularly, to the transfer of liquid helium from a stationary cylinder to a generator rotor.
In recent years, the science of cryogenics has expanded dramatically in the field of electrical power generation. Electrical generators are now being developed that have virtually eliminated the losses that are inherent when an electric current is transported through a resistive conductor. This progress has been made possible through the supercooling of the field windings of the generator's rotor. When these conductors are cooled to superconducting temperatures they exhibit a lack of resistance and allow transportation of field current with virtually no losses.
This supercooling of the generator rotor is typically accomplished by submersing the rotor's field coils in a pool of liquid helium which boils and thereby reduces the winding to superconducting temperature. Since the rotor, spinning at high speed, requires a constant replenishment of the liquid helium which has boiled off, a method of efficiently transferring liquid helium from stationary equipment to the spinning rotor is necessary. Typically this transfer is accomplished by disposing a stationary supply tube coaxially within a rotating inlet pipe which is connected to the rotor. This method creates a cylindrically shaped clearance gap between the tube and the pipe which is subjected to extreme temperature gradients across its length. These gradients can cause rapid oscillations between the liquid and gaseous states of the helium and it is to the elimination of these oscillations which the present invention is directed.
The transfer system disclosed herein provides a threaded insert in the rotating inlet pipe which, in response to the pipe's rotation, causes the liquid helium to be pushed inward towards the rotor's helium reservoir and, thus, away from the cylindrically shaped clearance gap which is between the rotating pipe and the stationary supply tube. This threaded member and the selective placement thereof not only drives the helium toward the reservoir during normal operation but provides the additional beneficial function of facilitating a reverse flow of helium into the stationary tube during fault conditions.
The problem of liquid coolant entering the cylindrically shaped clearance gap is addressed in U.S. Pat. No. 3,991,588, issued to Evangelos T. Laskaris on Nov. 16, 1976. The Laskaris device uses a step in the inside diameter of the rotatable supply pipe which is intended to permit only gaseous helium to enter the clearance gap.